In 1943, a pediatrician discovered a strange, previously uncharacterized disease. The pediatrician described the patients’ peripheral blood smears as containing abnormally large, distended granules, a first-in-man observation (1, 2). Clinicians in Cuba and Japan corroborated these findings, reporting similar childhood cases unified by three hallmark features: oculocutaneous albinism, granule abnormality, and death in early childhood (3, 4). This disease came to be known as Chédiak-Higashi Syndrome (CHS) (5, 6). In the ensuing decades, the lysosomal trafficking regulator (LYST) has emerged as the gene underlying CHS. While LYST initially garnered attention due to its connection to CHS, researchers identified LYST as a pivotal player in cellular and immune functions. Discovering CHS marked the beginning of decades of efforts to understand LYST’s role in biology and eventually its implications for human health and disease.

For decades following the landmark discovery, the scientific community was puzzled by this abnormal disease. While no one understood the etiology of disease, it was clear that CHS caused immune dysfunction and granule anomalies that warranted further investigation. These investigations eventually led to identifying the enlarged intracellular inclusions as being lysosomal in origin (7–9). Following the discovery of CHS, similar phenotypes were reported in animal models ( Table 1 ). Many seminal publications that provide insights into LYST molecular function involve the mouse homolog of LYST, beige, which has a phenotype that closely resembles human CHS. This model is discussed in more detail in section III. Animal models of LYST mutations. Human samples and animal models provided tools to examine the consequences of CHS on immune function and molecular biology, but efforts were limited by the unidentified cause of CHS. It was not until 1996, forty years after the first description of CHS, that researchers identified and cloned the causative human LYST gene (19, 20), which consists of 53 exons and is located on chromosome 1q42.1-1q42.2 (21).

After identifying the causative gene, researchers began dedicating efforts to understanding a place for LYST in cellular biology. Some groups focused on clarifying whether LYST causes granule abnormalities through fusion or fission processes (8, 22–28). Other groups were interested in potential binding partners of LYST that could suggest how LYST is involved in membrane dynamics and vesicle trafficking (29, 30). The journey to understanding LYST has extended into the 21^st century. With time, more tools have become available for studying LYST function. Recently, sequencing and structural analysis provided a more detailed molecular understanding of the LYST gene and protein structure (31, 32). These advancements provided more clues for its involvement in a myriad of cellular processes. Over the past decade alone, LYST has been linked to human health outside of CHS through connections to cancer and wound healing (33–40).

Despite longstanding interest in investigating LYST, a complete understanding of LYST biology is yet to be established. Here, we provide a comprehensive literature review to consolidate available scientific endeavors in relation to LYST, which may be of great value to the basic science and clinical community.

Following the initial discovery of the CHS, researchers published additional reports discussing clinical cases. The connection of LYST to CHS prompted further efforts to understand LYST function, which ultimately revealed its involvement in cellular biology and human health outside of CHS-related conditions. This autosomal recessive disorder presents along a clinical spectrum characterized by hypopigmentation, recurrent bacterial infections, developmental delays, and coagulation defects (41–43). Over 80% of patients reach the “accelerated phase” of the disease, wherein they develop life-threatening hemophagocytic lymphohistiocytosis (HLH), a hyper-inflammatory disorder associated with recurrent viral infections. This phenomenon represents the most common cause of death in patients with CHS (1, 2). Hematopoietic stem cell transplant is the only available curative treatment for CHS. Case studies demonstrated its potential in correcting immunologic complications and extending lifespan into adulthood (44). Yet, patients who survive into adulthood develop progressive central and peripheral neurodegeneration. A paucity of literature exists surrounding CHS, and while the exact prevalence is unknown, there have been fewer than 500 reported cases worldwide since its discovery (45, 46).

Animal models are critical for gaining further insight into the pathophysiology of LYST mutations. The most investigated animal models are murine equivalents of CHS. A radiation-induced mutation resulted in the first described Lyst-mutant mouse, deemed the beige (bg or Lyst ^bg) mouse for its silvery-grey coat coloration compared to C57BL/6J wild-type (WT) mice (47, 48). The spontaneous mutation of beige allele is caused by either i. 3-bp deletion of a single amino acid (isoleucine) within WD40 domain, or ii. a LINE1 element insertion, resulting in a truncated Lyst protein lacking both WD40 and BEACH domains (49). The genetic details are more thoroughly described in section VII toward a molecular understanding of LYST. Today, researchers use the beige-J (Lyst ^bg-J) strain, which is a spontaneous re-mutation virtually identical to the originally reported Lyst ^bg mice (10). Lyst ^bg-J and the less commonly used Lyst ^bg-2J mice, are phenotypically identical to the original Lyst ^bg mouse (10). Murine beige-grey mutant (Lyst ^bg-grey) mice carry a chemically induced Lyst mutation (discovered in an ENU mutation screen) that results in an unstable Lyst protein caused by Exon 25 skipping (11). Thus, unlike Lyst ^bg and Lyst ^bg-J mice, the beige-grey mutation leaves the WD40 and BEACH domains intact (11). Notably, all Lyst-mutant mice exhibit phenotypes commonly seen in human CHS patients, including abnormal pigmentation of coat color comparable to oculocutaneous albinism in human, immunodeficiency associated with abnormal or defective NK cells, and enlarged granules ( Table 1 ). The differential inclusion and/or exclusion of WD40 repeats, the BEACH domain, and Exon 25 result in a variety of Lyst-mutant transcripts and a spectrum of unstable Lyst proteins, potentially mirroring the spectrum of disease severity observed in human CHS patients.

A murine missense mutation (Lyst ^Ing3618) located in Exon 48 of the WD40 domain caused a progressive neurodegenerative phenotype, and the mouse lacked the immunodeficiency observed in beige mice (12). Lyst ^Ing3618/Lyst ^Ing3618 mice display progressive Purkinje cell degeneration and impaired neurological functions during aging compared to WT mice (12). By 18 months, the Lyst ^Ing3618 mice have enlarged lysosomes and almost no detectable neuronal Purkinje cells. This phenotype resembles the mild, atypical forms of CHS, characterized by early neurodevelopmental issues in childhood followed by progressive neurodegeneration in adulthood (50). Many other animal models possessing CHS-equivalent diseases resulting from Lyst mutations have also been reported ( Table 1 ), including mink (51, 52), cat (53–55), fox (56, 57), Wagyu cattle (58), corn snake (16), and rat (59).

Together, the beige mutant mice and related strains present a compelling experimental paradigm wherein the relative contributions of intact WD40 or WD40/BEACH domains to Lyst-dependent mechanisms could be interrogated in vivo to better understand LYST function in humans. We anticipate that these models could not only be used for understanding CHS pathology but also for investigating defective vesicular trafficking.

Much of what is known about LYST comes from the cell type-specific manifestations of LYST dysfunction observed in disease. LYST underlies the vesicle trafficking responsible for mobilizing specialized LROs that are central to host defense. In parallel with characterization of Lyst-dependent molecular mechanisms, investigations into the cell type-specific mechanisms demonstrated the extensive manifestations of defective endolysosomal trafficking. Enlarged granules have been observed in LYST-mutant NK cells (60), cytotoxic T cells (61), B cells and helper T cells, neurons, neutrophils/granulocytes, monocytes/macrophages, fibroblasts, platelets, and pigment-producing cells. Available evidence regarding each cell type is discussed in the following section, a graphical overview of which is provided in Figure 1 .

Initial and continued pursuits toward understanding the effect of LYST mutations focused on the pathognomonic hallmark described at the initial discovery of CHS: stark changes in the morphology and function of secretory lysosomes.

Peripheral blood leukocytes from CHS patients underwent extensive examination using light microscopy and various staining techniques. Initially, the enlarged bodies in peripheral blood neutrophils were thought to be giant peroxidase granules, Döhle bodies, and azurophilic clumps (4, 5, 116). Subsequent technological advancements in electron microscopy and immunofluorescence led to the discovery that the enlarged bodies were, in fact, lysosomes, supported by the morphological characteristics, localization, and acid phosphatase activity (7–9). Further investigation extended this understanding to beige and CHS fibroblasts, revealing acid phosphatase-positive intracellular inclusions containing the lysosomal markers, alpha-2-macroglobulin and rhodamine (23, 24, 117, 118). Lysosomal origin was also confirmed in various cell types including beige osteoclasts, gastric chief cells, parietal cells, and renal proximal convoluted tubal cells with enlarged granules (119–121). Recent studies consistently affirmed the identity of the enlarged inclusions using specific lysosomal markers including lysosomal-associated membrane protein-1 (LAMP-1), LAMP-2, and Rab7 (40, 64, 87, 122–124).

Lysosomes are dynamic organelles that operate at the intersection of the endocytic and secretory pathways. Lysosomes originate from transport vesicles budded from the trans-Golgi network, and these vesicles periodically fuse with endosomes to degrade material. Early endosomes are specialized compartments that receive material from the extracellular environment through processes like endocytosis. Early endosomes transition into late endosomes, marked by a conversion of the small GTPase Rab5 to Rab7 (125, 126). Late endosomes fuse directly with lysosomes, forming a hybrid organelle that acts as a site for degradation. Lysosome populations reform from these hybrid organelles. Lysosomes undergo fusion with one another, other intracellular compartments, or target membranes facilitated by docking proteins, including SNAREs, Rab GTPases, and Rab effector proteins (127). Lysosomes are critical for macromolecular degradation and recycling, intracellular protein and vesicle trafficking, and cellular signaling (127). Lysosome related organelles (LROs) are similar to lysosomes, and some cells utilize LROs for lysosomal functions (128). While the LROs originate from the endolysosomal system, certain cells including neutrophils and melanocytes harbor specialized LROs such as azurophilic granules and melanosomes.

While the mechanisms of lysosome biogenesis are well-defined, the role of LYST in these processes remains incompletely understood. Lysosome numbers and size are maintained by a steady state of fission and fusion events (129). Dysregulation of fusion and fission manifests as morphological changes to lysosomes and LROs. Fusion with endosomes increases lysosome size by incorporating vesicle content and membrane material (28), while fission leads to fragmentation and size reduction. LYST is hypothesized to affect lysosomes and LROs by either i. limiting the fusion or ii. promoting the fission of endolysosomal organelles (23, 24, 26).

The first hypothesis is that the enlarged lysosomes arise from excessive fusion events (8, 22–26). Time course tracking of lysosomes in cultured CHS cytotoxic T lymphocytes demonstrated that over the course of 9 days, normal-sized lysosomes clustered around the nucleus and aggregated to form the characteristic enlarged structures found in LYST mutant cells (68). The greatest support for LYST’s potential inhibitory effect on lysosome fusion came from investigations into the Dictyostelium ortholog of LYST: large volume sphere B (lvsB). In lvsB-null cells, the endolysosomal fusion and phagosome-phagosome fusion events were significantly increased as measured using a fusion assay (130). Further investigation found that lvsB antagonized the activity of the DdRab14 protein, a GTPase with pro-fusion activity (124). While the lvsB-mutant cells could not prevent the fusion of lysosomes with post-lysosomes, they did not affect the fusion of post-lysosomes with early endosomes (124). Post-lysosomes are secretory vesicles destined for exocytosis, indicating that the role of lsvB in inhibiting lysosome fusion is specific to certain cellular compartments and does not affect the fusion events involving early endosomes. This suggests a nuanced and targeted regulatory mechanism where lsvB selectively modulates lysosomal fusion processes, highlighting the complexity of intracellular trafficking and secretion pathways in the context of lvsB and DdRab14 protein activity. LYST-related fusion/fission dynamics were further explored by comparing lsvB null cells with two well characterized fission defect mutants, µ3-null and WASH-null cells. lsvB-null cells exhibited increased multi-particulate phagosomes compared to the fission defect mutants and WT cells. Tracking lysosome maturation with latex beads also showed a deceleration in particle transfer in the IvsB null cells. Ultimately, only lysosome fusion with post-lysosomes was impacted by absence of lsvB (124). In a follow-up examination, IvsB mutant revealed significantly enlarged lysosomes and decreased post-lysosomes. However, the authors were unable to claim whether fusion dysregulation caused the enlarged lysosomes (15, 131).

A competing model establishes LYST and its homologs as a positive regulator of fission events, the second hypothesis for LYST’s effects on lysosomes. Experiments in murine fibroblasts demonstrated that Lyst overexpression led to the reversal of the enlarged lysosomal phenotype, yielding smaller-than-normal lysosomes with no observed effects on lysosomal fusion (27). Since fusion was unimpacted, overexpressing murine Lyst may have corrected the diseased phenotype by promoting fission events. Beige bone marrow derived macrophages were treated with acetic acid to fragment lysosomes. Upon withdrawal, beige lysosomes re-fused with no delay compared to WT cells. Then, CHS and beige fibroblasts were treated with vacuolin-1 to cause lysosomal swelling. The swelled lysosomes in beige fibroblasts recovered slower compared to WT fibroblasts, yet overexpression of Lyst increased lysosomal size recovery (27). Findings from these experiments led the authors to conclude that mutations in LYST impact lysosomal fission, not fusion (28). Similar findings are also observed in a C. Elegans study, in which disrupting the LYST ortholog, Lyst-1, resulted in decreased lysosome size. To determine if this was attributable to defects in lysosome fusion, the authors created double knockouts for Lyst-1 and Cup-5, which is a known lysosomal fission regulator necessary for limiting lysosome size. In Cup-5 mutants, disrupting genes known to be involved in lysosomal fusion suppressed lysosome enlargement (73). The Lyst-1/Cup-5 double mutant, however, did not experience a reduction in lysosome size, leading authors to conclude that Lyst-1 was not involved in lysosome fusion (14).

While other studies contributed additional insights into LYST-associated abnormal granules, they have not definitively concluded whether LYST mediates lysosome morphology through fusion or fission events. In the context of CHS, cytotoxic T lymphocytes exhibited abnormal localization of necessary effectors for lytic granule exocytosis, Muncl3-4, Rab27a, and Slp3, within enlarged intracellular organelles. Overexpression of these effectors restored degranulation in the CHS mutant cells, indicating that LYST mutations impaired the maturation of pre-secretory granules to secretory granules. However, the specific influence on lysosome fusion or fission events remained undetermined (123). In a Drosophila study investigating a LYST ortholog mutation, Mauve, researchers found that the enlarged lysosomal related organelle in Mauve-mutants resulted from uncontrolled late phagosome homotypic fusion prior to fusing with lysosomes. Ultimately, the data could not distinguish whether this was due to LYST regulation of fusion or fission events (13).

The story of LYST and its place in cellular biology is enigmatic, characterized by extended gaps between publications. The compromised immune system that is characteristic of Chédiak-Higashi Syndrome is associated with enlarged lysosomes in various immune cells. While LYST mutations do not prevent activation of immune cells, the functional defects seem to be caused by impaired polarization of these enlarged lysosomes or granules to the immunological synapse (61, 132).

To explain the impaired polarization, some groups detailed apparent defects in microtubule (MT) organization in LYST-mutant cells. Oliver and colleagues investigated the formation of concanavalin caps on polymorphonuclear leukocytes (PMNs) and differences in capping behavior in WT and LYST-mutant mice (133). The study revealed that when various cell types are treated with concanavalin A (conA), lectin aggregates into one region of the cell, thereby forming a cap. Colchicine is an anti-mitotic agent that is known to disrupt microtubule polymerization and assembly, which is necessary for vesicle trafficking. PMNs from WT mice only cap with ConA after colchicine treatment, whereas PMNs from Lyst-mutant mice cap spontaneously. The similarity between LYST-mutant PMNs to colchicine-treated cells suggests a potential link between the mutant LYST phenotype and microtubule instability or dysfunction. Interestingly, this spontaneous surface cap formation was not unique to mice, as further studies indicated the abnormality in human peripheral blood PMNs from Chédiak-Higashi patients. This abnormality is linked to impaired microtubule function, which could be due to issues in 3’,5’ cyclic guanosine monophosphate (cGMP) generation. Indeed, treatment with cGMP decreased cap formation in LYST-mutant cells.

The investigation surrounding the role of LYST in microtubule function gained momentum with the discovery that beige mice exhibited an impaired mu-opioid and kappa-opioid receptor-mediated analgesic response to morphine (134, 135). This was one of the few studies that explored the role of LYST in neurological systems. The study discovered that impaired response to morphine was independent of receptor number or binding affinity, indicating the strain-dependency of the impaired response to morphine (136). The authors speculated that this was a consequence of disrupted membrane-related microtubular function in beige mice. Beige mice were given cholinergic agonists, which restored the analgesic response to morphine (137). This serves as the only evidence that the beige-specific impaired response to morphine was related to microtubular dysfunction. More recent studies provided definitive evidence that Mauve was necessary for microtubule nucleation during cell division (122).

While some studies support that the LYST mutations adversely affect microtubule function, other groups found intact MT function in addition to normal number, length, and distribution (138, 139). Despite normal MT function, both large WT lysosomes and abnormally enlarged lysosomes in LYST-mutant cells were unable to migrate through the cytoplasm due to their size (140). Thus, a new hypothesis emerged postulating that lysosome and granule dysfunction arose not from microtubule (MT) impairment but potentially from alterations in lysosomal motility due to abnormally enlarged size. This thought prompted further investigations into the intricate molecular mechanisms underlying LYST mutations and their broader implications in cellular processes.

Researchers further explored the role of LYST in lysosomal membrane dynamics. SNAREs (Soluble N-ethylmaleimide-Sensitive Factor Attachment Protein Receptors), are key proteins involved in membrane fusion processes, facilitating the docking and fusion of vesicles with target membranes. Some studies suggested that the connection between LYST and SNARE complex assembly and function could lead to abnormal lysosome morphology and lysosomal dysfunction observed in LYST-mutants. Yeast two-hybrid screening revealed several potential LYST binding partners including calmodulin (CaM), casein kinase II (CK2), 14-3-3, and Hepatocyte growth factor regulated tyrosine kinase substrate (HRS) (29). These proteins are well described members of the SNARE complex responsible for mediating cellular membrane fusion events such as exocytosis, vesicle transportation, and signal transduction ( Table 2 ) (30). It is worth noting that additional experiments are necessary since the authors were unable to validate the binding partners in their study.

The leading hypothesis was that LYST acts as a scaffolding protein facilitating critical interactions between SNARE complex proteins through regulation of Synaptotagmin and Protein Kinase C (PKC):

LYST is a member of the class of “BEACH domain-containing proteins” (BDCPs) (31). The Beige and Chédiak-Higashi (BEACH) domain is a highly conserved region first identified within the LYST protein but present in all other BDCPs. BDCPs regulate a variety of cellular functions, such as synapse formation regulated by neurobeachin (NBEA) and granule size regulated by beige-like anchor protein (LBRA) and LYST (31). Other BDCPs are also involved in vesicle trafficking and membrane dynamics in humans (31). Mutations in BDCPs cause several complications including epilepsy (NBEA mutation), grey platelet syndrome (NBEAL2 mutation), and rare autoimmune diseases (LRBA mutation) (155–157). Current consensus suggests that BDCPs, including LYST, act as cytosolic scaffolding proteins that facilitate membrane events involved with vesicular trafficking (31).

Recent advancement in molecular technologies further promoted understanding of the molecular aspect of LYST. The LYST protein is comprised of 3801 amino acids (158), but alternative splicing yields multiple transcript variants (documented in RefSeq). Generally, LYST contains an ARM/HEAT domain followed by a ConA-like lectin domain, a pleckstrin homology-like (PH-like) domain, a highly conserved BEACH domain, and finally, C-terminal WD40 repeats (31, 159).

Even though current literature lacks studies into the biological functions of each domain, protein structural analysis revealed possible functions related to each domain. ARM/HEAT repeats have been shown to mediate vesicle trafficking and lipid binding (132, 160, 161). The PH domain has a central fold associated with membrane binding to specific proteins (162). The crystal structure of the 130-residue segment N-terminal to the BEACH domain reveals a backbone fold with a PH domain and an extensive interface between BEACH and PH domains (31). Consistent with these structural analyses, protein binding assays demonstrated that the PH and BEACH domains strongly interact with one another in vitro and in silico (32). LYST contains an 8-15 amino acid insertion in the BEACH domain that differentiates its function from the other BDCPs (31, 163). Interestingly, a Lyst-specific BEACH function that determines lysosome and granule size likely exists. In mouse cells, protein truncation of only the Lyst-BEACH C-terminal fragment, but not the Nbea-BEACH C-terminal fragment, led to reversible lysosome enlargement (31, 163).

The parallel advancements in murine reagents and DNA sequencing contributed much of the genotype and phenotype correlations reported to date. A comprehensive literature review was conducted, involving a systematic search of peer-reviewed articles and case reports associated with “LYST” and “Chédiak-Higashi Syndrome” through the PubMed database (https://pubmed.ncbi.nlm.nih.gov/advanced/). We analyzed 29 case reports related to CHS, involving 61 patients ( Figure 2 , Supplementary Table 1 ) to explore the potential connection between LYST mutant genotypes and clinical manifestations of the disease. The genetic investigations suggest a link between the nature of the mutant LYST gene and the severity of the disease. For instance, it was observed that nonsense mutations, which typically result in the production of a truncated LYST protein, are associated with more severe phenotypes and often lead to infant mortality. In contrast, missense mutations tend to be linked to milder phenotypes or a later onset of the disease. A recent study by Morimoto and colleagues found comparable connections between the type of mutation and disease severity, providing additional support for genotype-phenotype correlations (164).

Further analysis indicates that the location of the mutated nucleotide(s) with respect to protein structure, in addition to mutation type, more closely correlates with disease phenotype ( Figure 2 ). For example, mutations occurring within the ARM/HEAT repeats are associated with albinism, while neurological disorders are connected to mutations in the ConA-like lectin domain. Nonsense mutations within the WD40 domain are likely contributors to severe immune dysfunctions in CHS, leading to the accelerated phase, as depicted in Figure 2 . Notably, ARM/HEAT mutations have been reported more frequently than mutations in other domains due to the domain’s larger size. However, a lack of data regarding the BEACH and WD40 domains may introduce potential inaccuracies in the interpretation of their functions.

Furthermore, it is important to highlight that the precise location of the ARM/HEAT repeats has not been definitively confirmed, despite proposed by Nagle et al. suggesting that these repeats may extend across a substantial helical region (31).

LYST was recently established as a gene of interest in patients with acute myeloid leukemia (AML), colorectal cancer, epithelial ovarian cancer, multiple myeloma, pulmonary carcinosarcoma, and sporadic chordoma (33–39). The association of LYST mutations with various forms of cancer is a chance discovery stemming from next generation sequencing analysis. Currently, the trend seems to be that downregulation or truncation of LYST protein leads to cancer progression. Downregulation of LYST was associated with low survival of AML patients, but in calcitonin receptor-like receptor (CALCRL) knockdown AML cell lines, LYST was upregulated (33). CALCRL deficient cells have been shown to be resistant to chemotherapy. The authors postulated that CALCRL downregulates LYST expression, which enlarges and stabilizes lysosomes and enhances drug resistance. In patients with sporadic chordoma, many patients carried truncating mutations in LYST. The authors explained that lysosomes were recently determined to be important for notochordal development, which could explain why defective LYST led to chordoma development. LYST also localized within copy number aberration regions in patients with multiple myeloma (39). Silencing LYST expression using anti-LYST siRNA inhibited proliferation and induced apoptosis in multiple myeloma cells (34). Both missense and nonsense LYST mutations were associated with pulmonary carcinosarcoma (38). Currently, studies are correlative but not mechanistic; authors appear to be divided on whether the connection of LYST to cancer is a spurious correlation or if LYST mutations truly drive cancer progression.

Chédiak-Higashi Syndrome (CHS) is a rare and life-threatening disorder, particularly affecting children. Despite identifying the causative gene decades ago, there is no comprehensive understanding of the cellular and molecular mechanisms underlying LYST function. The limited therapeutic options, primarily hematopoietic stem cell transplant, highlight the urgent need for more effective treatments to halt disease progression and prevent childhood mortality.

Recent studies employing various LYST-mutant organisms not only provided opportunities to study CHS, but also contributed to the understanding of the cell-specific role of LYST in endolysosomal trafficking and the immune response. Animal and clinical research highlights how LYST mutations manifest clinically in the setting of CHS, demonstrating its importance in immunity, neurological functions, pigmentation, and blood coagulation. Generally, cells from affected systems exhibit abnormal LRO morphology, impaired polarization, and decreased intracellular mobility, leading to reduced exocytosis of granules and protein trafficking.

While existing literature lacks unified theories on how LYST affects cellular processes, previous research proposes intriguing mechanisms contributing to the consistently observed enlarged lysosomes in CHS. This review provides a summary of the potential role of LYST in microtubule dynamics, granule fusion and fission events, and membrane docking facilitated by SNARE complex proteins. The current body of literature is divided on whether LYST impacts granule size through fusion or fission. Some studies suggest upregulated fusion events causing abnormal morphology, while others argue for insufficient fission as the culprit. The enlarged lysosomes and LROs do not fulfill their biological functions, and some studies suggest that the observed dysfunction involves changes in microtubule dynamics that impair proper vesicle transportation. Contradictory findings indicate intact microtubule function and suggest that the abnormally enlarged lysosomes physically cannot transit the actin cytoskeleton.

Sequencing technology enhanced our comprehension of the molecular structure and potential biological function of LYST by identifying genetic mutations. Recently, 11 novel disease-causing LYST mutations in the BEACH domain were identified using targeted Sanger sequencing, thereby expanding the scope and depth of LYST research (164). These findings provided valuable insight into mutation pathogenicity, laying the groundwork for potential CHS therapies and next-generation immuno-modulatory treatments.

Further investigation into the mRNA and protein sequences of LYST and lesser-explored members of BDCPs, such as WD repeat domain 81 (WDR81), is necessary to clarify the sequences and the precise locations of their domains. LYST and other BDCPs have diverse cellular functions, including cell cycle control, transcription regulation, apoptosis, and vesicle trafficking (31).

Knowing how LYST exerts its effects on a cellular and molecular scale holds significance not only for the development of CHS therapies but for other diseases involving cell regulation and vesicle trafficking. LYST mutations appear to be associated with certain cancer types, yet its potential role in cancer is not yet understood. Cutaneous wound healing studies revealed LYST’s crucial involvement in regulating secretory exocytosis by fibroblasts, which sheds light on the broader impact of LYST function (56, 57). Moreover, LYST attenuated immunomodulation combined with tissue engineering may improve transplant performance. While in the early stage of investigation, the importance of LYST in immune signaling suggests that LYST may influence the foreign body response to transplanted material. Thus, targeted alteration and temporary modulation of LYST function could offer immune privilege to recipients and protect donor tissues from overactive immune responses and rejection. The SCID/bg mouse model, where the Lyst beige mutation is introduced in SCID mice, has improved xenotransplantation compatibility (165). Recent advancements in tissue engineering, such as Tissue Engineered Vascular Grafts (TEVG) attracted attention due to the capacity for growth and remodeling (166). Despite their success, clinical studies have identified stenosis as a primary limitation. The immunodeficient SCID/bg mouse model demonstrated a drastic improvement in TEVGs patency (166). In the realm of regenerative medicine, LYST immunomodulation emerges as a promising target, aligning with the evolving paradigm of “immune interactive” strategies over traditional “immune evasive” approaches.

The discoveries presented herein underscore the potential for LYST as a tool for understanding the intersection of vesicle trafficking and cell cycle regulation and harnessing these findings to inform immune-modulatory strategies.

MT: Conceptualization, Data curation, Formal analysis, Investigation, Writing – original draft, Writing – review & editing. JC: Conceptualization, Data curation, Formal analysis, Investigation, Writing – original draft, Writing – review & editing. GM: Investigation, Writing – original draft, Writing – review & editing. CK: Writing – review & editing. KB: Investigation, Writing – original draft, Writing – review & editing. SR: Writing – review & editing. JZ: Writing – original draft, Writing – review & editing. ChB: Conceptualization, Supervision, Writing – original draft, Writing – review & editing. CaB: Conceptualization, Data curation, Funding acquisition, Supervision, Writing – original draft, Writing – review & editing. JB: Conceptualization, Supervision, Writing – original draft, Writing – review & editing.